Field of the Invention
The present invention relates to temporarily storing a carrier in which semiconductor wafers or the like are housed.
Description of the Related Art
In order to improve the utilisation rate of semiconductor fabrication equipment, temporal storage apparatuses (buffers) are provided in the vicinity of load ports of semiconductor fabrication equipment. In this regard, Patent Literature 1 (JP 2012-111635) by the applicant has proposed to provide a travelling rail for a local vehicle in parallel with and below a travelling rail for overhead travelling vehicles (overhead hoist transports (OHT)). If buffers suitable for transfer between the local vehicle and between the overhead travelling vehicles are provided at positions under the travelling rail for the local vehicle and not over the load ports, for example, four buffers may be provided. If the buffers are not sufficient in its their number, then, providing the overhead travelling vehicles and the local vehicle with a lateral transfer mechanism for carriers and providing additional buffers at downward and sideway positions from the travelling rail for the local vehicle are a possible design for increasing the number of buffers.
Patent Literature 2 (WO 2013/183384) also by the applicant has proposed to remove interference between overhead travelling vehicles and a local vehicle by a mutual exclusion control through communication terminals. Namely, communication terminals are provided along a travelling rail for overhead travelling vehicles and a travelling rail for a local vehicle, and if an overhead travelling vehicle starts communication first, then, the local vehicle is prohibited from entering. If the local vehicle starts communication first, then, the overhead travelling vehicle is prohibited from performing transfer. Thus, a mutual exclusion control is performed such that the local vehicle does not enter into a position where an overhead travelling vehicle is transferring a carrier.